In many cases, a compressor used for a refrigeration cycle has a compression portion and a motor chamber inside an airtight container, where the compression portion is driven via a rotary drive axis of the motor. The compression portion compresses a low-pressure refrigerant let into an airtight operation chamber to a high-pressure refrigerant by reducing its airtight capacity.
As the compression portion drives at high speed and high temperature, lubricating oil is pooled in the bottom of the motor chamber. Under ordinary circumstances, the lubricating oil is supplied to a refrigerant compression chamber through a suction opening provided inside the rotary drive axis and lubricates a bearing of the rotary drive axis and a sliding surface of a refrigerant compressing portion to be returned thereafter to the bottom of the motor chamber by going through a waste oil passage inside a main frame.
When returning the lubricating oil having lubricated the compression portion to the bottom of the airtight container, there are the cases where, if the lubricating oil contacts discharge gas, it is discharged with the discharge gas outside the compressor. If a large amount of the lubricating oil is discharged outside the compressor, there is not only a possibility of causing mal-lubrication due to lack of the lubricating oil but also a possibility of reducing thermal efficiency of the refrigeration cycle due to the lubricating oil discharged to the refrigeration cycle.
As one of the methods for preventing this, Patent Document 1 (Japanese Patent Application Publication No. 2000-80990) for instance provides the waste oil passage inside the main frame of the compression portion so as to draw the lubricating oil directly back to the bottom of the airtight container via a waste oil pipe for securely returning the lubricating oil from the waste oil passage to the bottom of the airtight container.
As another method, Patent Document 2 (Japanese Patent Application Publication No. 2002-161880) for instance provides the waste oil passage radially (horizontally) on the main frame and inserts an L-shaped waste oil pipe into the waste oil passage to discharge the waste oil. It is thereby possible to further reduce leakage of the lubricating oil at a joint portion with the main frame.
In the case of the above-mentioned compressors, however, the following problem remains unsolved. To be more specific, the waste oil pipe of these prior arts is overhung, and so a free end side (tip side) oscillates due to oscillation of the motor and hits an internal surface of the airtight container, which is one of the causes of generating abnormal noise.
As for the method described in Patent Document 1 in particular, the waste oil passage is formed in an axial direction so that there is a possibility that the waste oil pipe may fall off due to the oscillation of the motor and so on even if it is fixed by press fitting.
As for the method for preventing this, Patent Document 1 forms a flange portion for a retaining purpose in a part of the waste oil pipe. However, forming the flange portion in the pipe requires higher cost and longer time for assembly work.
As for the method described in Patent Document 2, the waste oil pipe is L-shaped. Therefore, the axial direction portion (the portion vertically extending) of the waste oil pipe is apt to swing circumferentially on press-fitting the waste oil pipe to the main frame, and there is a possibility that it may be displaced on inserting it into a notch of a stator core and result in defective assembly. Furthermore, even if the L-shaped waste oil pipe is press-fitted and fixed on the main frame, there is a possibility that the press-fitted portion may get loose and fall off if the waste oil pipe is touched in a following assembly stage.
There is also a method for preventing this oscillation whereby a part of the waste oil pipe is fixed by a subframe or the like provided on the bottom side of the airtight container. It cannot be denied, however, that fixtures for fixing it require cost and assembly work takes a lot of effort.